Evaluating the End-User Experience of Private Browsing Mode
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Nowadays, all major web browsers have a private browsing mode. However, the mode's benefits and limitations are not particularly understood. Through the use of survey studies, prior work has found that most users are either unaware of private browsing or do not use it. Further, those who do use private browsing generally have misconceptions about what protection it provides. However, prior work has not investigated why users misunderstand the benefits and limitations of private browsing. In this work, we do so by designing and conducting a two-part user study with 20 demographically-diverse participants: (1) a qualitative, interview-based study to explore users' mental models of private browsing and its security goals; (2) a participatory design study to investigate whether existing browser disclosures, the in-browser explanations of private browsing mode, communicate the security goals of private browsing to users. We asked our participants to critique the browser disclosures of three web browsers: Brave, Firefox, and Google Chrome, and then design new ones. We find that most participants had incorrect mental models of private browsing, influencing their understanding and usage of private browsing mode. Further, we find that existing browser disclosures are not only vague, but also misleading. None of the three studied browser disclosures communicates or explains the primary security goal of private browsing. Drawing from the results of our user study, we distill a set of design recommendations that we encourage browser designers to implement and test, in order to design more effective browser disclosures.
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